Mice of the STR/N strain show evidence of a primary polydipsia and polyurea and undergo a progessive loss of alveolar bone with increasing age. Due to severe hydronephrosis and the formation of an urethral plug, male mice of the STR/N strain are not suitable for long term studies. The female mice which also have a primary polydipsia and polyuria, rapidly develop very high bone fluoride concentrations when provided with drinking water containing 50 ppm of fluoride. At 5 and 7 months of age STR/N mice with a very high skeletal fluoride load (1.5% F on an ash basis) were found to excrete 77% of a fluoride challenge in the urine whereas mice the same age with a low skeletal fluoride content (0.006 - 0.008%) excreted only 54.5%. There was no effect of fluoride intake on the weight, length, width or on the breaking strength of the bone. Additional data is being collected on alveolar bone loss to complete these studies.